This invention relates to additive compositions, also known as admixtures, for incorporation in hydraulic cement mixes, for example, hydraulic cement concretes, mortars, grouts, neat cement mixes, nonplastic cement or concrete mixes, such as concrete block mixes, and dry mixes for making such concretes, mortars, and grouts, and more particularly, to the use of such admixtures for improving the compressive strength of products made from such cement mixes. The admixtures of the present invention are glycol acetates, which are acetic acid esters of glycols, and a preferred admixture of the present invention is ethylene glycol diacetate.
Many materials have been used as admixtures for improving the compressive strength of hydraulic cement mixes. In accordance with ordinary usage, it will be understood that references to the strength of hydraulic cement mixes actually refer to the strength of products produced from such mixes after setting and hardening by reaction with water. Among the more commonly used strengthening admixture materials are the lignosulfonates, such as calcium lignosulfonate; salts of hydroxycarboxylic acids; sugars such as glucose (dextrose), maltose, fructose, and the like; and highly polymerized polysaccharides, such as dextrins. In general, these admixtures also reduce the amount of water needed in the hydraulic cement mixes, such water reduction usually resulting in increased compressive strength.
Another effect of the use of these admixtures has generally been the retardation of the rate of setting and hardening of the cement mixes in which they are used. This effect is believed to be the result of a slowing of the chemical process of hydration, so that concrete remains plastic and workable for a longer time than concrete without such a set retarder. Admixtures having set retarding properties are useful as set retarders per se, for example, to delay the set of cement during difficult placements that require the concrete to be in a plastic condition for a longer than normal period of time or to overcome undesired acceleration of set during hot weather. When such set retardation is desirable, then the above admixtures which both improve the strength and retard the set of cement mixes are suitable.
However, frequently there are instances where any significant retarding of the rate of hardening of the cement or concrete mix would be undesirable, or where an acceleration of the set is desired. For example, acceleration may be desired when concrete is to be placed during very cold or even freezing weather conditions, or when minimizing set time is important such as in laying a roadway where use is desired as soon as possible. In instances where both increased strength and set acceleration are desired, it has often been necessary to add a set accelerator in combination with the strengthening admixture. Well-known accelerators are calcium chloride and alkanolamines such as triethanolamine, both of which increase the rate of hydration for early strength development. However, the use of chlorides can lead to a corrosion problem when the concrete is in contact with metal materials. For this reason, chlorides are generally prohibited in prestressed concrete. In addition, many of the known accelerators, such as the alkanolamines and triethanolamine are very expensive and of limited availability. Low molecular weight aldehydes and polymers thereof, for example paraformaldehyde or Paraform, are known to be strong accelerators, but in aqueous solution such materials evolve esthetically objectionable and toxic fumes. As a result, the quantity of these materials that can be incorporated into concrete is very limited.
As will be discussed in detail hereinbelow, the admixtures of the present invention are a class of chemicals known as glycol acetates, which are acetic acid esters of glycols. The use of glycols per se as cement additives is discussed in Bechtold U.S. Pat. No. 2,225,146, Dec. 17, 1940 in which the glycols are used as grinding aids in the production of cement from cement clinker. Another patent, Harada et al U.S. Pat. No. 4,060,425, Nov. 29, 1977, discusses the use of glycols to increase the strength of specially formulated cement base mixtures designated as "super rapid hardening mixtures". Another class of acetic acid esters which have been used as cement additives are the acetic acid esters of glycerol, which are discussed as cement clinker grinding aids in Bechtold U.S. Pat. No. 2,203,809, June 11, 1940.
The aforementioned patents relate to chemicals which are in some ways similar in chemical structure to the glycol acetates of the present invention but which are nevertheless chemically distinct. However, none of these patents is directed toward providing cement admixtures which increase the strength of cement mixes while also providing the unique combination of additional advantages which will now be discussed.